Emptying Pit Latrines

MOBILE NOTE 27 Emptying pit latrines Introduction Well-managed pit latrines offer an effective, safe and hygienic way of containing excreta at relatively low cost. Excreta decomposes in the pit, which will eventually fill up and need to be emptied. This note considers the principal issues relating to safely removing excreta from a pit. The note is specifically concerned with dry systems, rather than septic tanks and cesspits. Contents Introduction ....................................................1 Suitable method .............................................3 Avoiding the need to empty pits ....................3 Emptying a single pit latrine ..........................9 Disposing of faecal sludge ...........................19 References ...................................................23 About this note .............................................25 Suitable method Choosing the most suitable method of emptying excreta from a pit is determined by: • the actual cost to the household (how affordable it is and therefore how likely it is that the household will pay for the service); • the relative cost of building a new latrine against the cost of emptying the existing one; • the health impact on workers; • the type of latrine to be emptied; • the type of pit lining; and • how the excreta will be disposed of. Avoiding the need to empty pits Move the latrine If there is sufficient space, one solution is to construct shallow pits (less than a metre deep) and relocate the latrine superstructure, or build a new one, when the pit is almost full – rather than empty the pit. With the superstructure and pit cover moved for reuse, or demolished, a tree can be planted in the pit. The tree makes use of the nutrients in the excreta and can yield a good crop. This latrine system is often referred to as an Arborloo. To be affordable, the superstructure should be either easy to relocate, or made of local materials that are easily replaced. Bucket latrines Bucket latrines are not a recommended sanitation option. However, in some circumstances such as short-term emergency response, or in highly flood- prone areas, they may be the only viable short-term option. As bucket latrines are emptied on a frequent basis (often daily or weekly), the fresh excreta must be handled extremely carefully. This is an unpleasant and unhealthy task. Additives Certain chemical and biological additives claim to enhance decomposition of excreta, but this only extends the time between emptying pits, rather than addressing the challenge of emptying pits altogether. Warning! Additives must be handled with extreme care. Emptying alternating pits Alternating ‘twin-pit’ pit latrines make use of the same pits on a rotational basis. This means that a permanent superstructure can be used. Two pits are dug, each sized to store about two year’s worth of excreta. Each pit has a removable cover slab, providing access to the pit. One pit only is put into use and filled over time. Once this pit is full, it is closed off for storage, while the second pit is used. As the second pit fills, the first pit is emptied and put back into use (Figure 1). Side view Inspection chamber Handles for pit and inspection chamber covers Pan Water trap >d d (if fitted) d = depth of pit Connecting pipe Approx. 1m Top view Pit 1 not in use Approx. 1m Inspection chamber with stone or block of wood for >d blocking secondary pipe Pit 2 in use Figure 1. Twin-pit latrines Given the right conditions of temperature, moisture content and pH, after 2 years storage the excreta will have decomposed and the disease- causing organisms died off sufficiently that the excreta to be manually handled. The stored excreta may look like soil, but it should still be handled carefully to minimize health risks associated with any incorrect use of the latrine. Manual emptying often involves someone entering into the pit, so they should be equipped with ladders, ropes, protective clothing, shovel and buckets as a minimum. Composting and dehydrating latrines Latrines can be designed and used in a way that speeds up excreta decomposition and makes emptying easier. Examples are composting and dehydrating latrines. Two pits are typically used in a composting latrine, with one left unused for the excreta to decompose while the other is in use. With dry material (such as wood ash or soil) added to the faeces they can decompose, and the pathogens die-off more rapidly. Composting latrines require more day-to-day management by the user and usually have to be emptied more frequently than simple pits, but emptying tends to be easier, with reduced (but not removed) associated health risks. In dehydrating latrines, urine is diverted away from the pit into a separate collecting vessel, or to a soakaway (Figure 2). The removed faeces can be used, with care, as a soil conditioner for certain crops. Both types require excreta reuse to be socially acceptable, with the faeces carefully removed and transported to the field and correctly applied to the land, ideally where children do not play (WELL, 2006a). Drop hole with tight-ﬁtting cover Door for emptying compost Urine collection pot or open system to soakway Figure 2. Twin-pit urine-diverted composting latrine Emptying a single pit latrine Where a single pit that is continually in use is to be emptied, two techniques can be used: mechanical pumping and manual emptying. The pit should be fully lined, especially where mechanical emptying is to take place, as the removal of the semi-liquid material may cause unlined pits to collapse. A single shallow pit will need emptying more frequently than a more expensive deep pit, but this may suit the finances of the household – who may be reluctant to save up for many months to pay for the evacuation of a deep pit. Regular emptying of shallow pits however needs to be supported by a responsive service, especially in urban areas (WELL, 2006b). Mechanical pumping Mechanical emptying systems exist that are both technically and financially viable, but these are typically the services provided by local sewage operators in the more formal areas of towns and cities, using large conventional vacuum tankers to empty both pits and septic tanks (Figure 3). Inspection hole Vacuum pipeline Suction inlet Pipe Manhole cover Vacuum pump Suction inlet valve © WEDC Discharge outlet valve Figure 3. KenA Chattertonconventional © WEDC Loughborough vacuum University tanker To address the challenge of providing mechanized pit emptying services in informal areas and slums, a low- cost technical solution has had to be developed. The solution is portable vacuum tankers, specifically designed for use in slums and other areas that are difficult to reach with a conventional vacuum tanker. Portable tankers are currently used in informal settlements and slum areas of Dhaka (Bangladesh), Nairobi (Kenya), Maputo (Mozambique), Dar es Salaam (Tanzania) and other cities (Figure 4). Vacuum pump and guage Extractor pump motor (reversible to blow out tank contents) Discharge outlet valve Towing bracket Suction inlet valve © WEDC Figure 4. Features of a portable vacuum Kentanker Chatterton © WEDC Loughborough University One of the most successful attempts in recent years to develop hand-operated machines for pit emptying was in Tanzania. The tankers were made of local materials based on the standard oil drum. To date, results have been promising but they have only been used for wet pits containing no solids (Figure 5). Handle Pump operated by turning hand wheel Handle Vaccum © WEDC pipe Connection also used as waste outlet for Waste Inlet disposing of drum contents Vaccum pump Waste disposal cart Ken Chatterton © WEDC Loughborough University Figure 5. Hand-operated vacuum tankers Vacutug The Vacutug is probably the most widely used small vacuum tanker operating in informal settlements. The original module was designed by Manus Coffey Associates (with support from UN Habitat) for use in Kibera, Kenya in the late 1990s. The first Vacutug has a 500 litre capacity tank and vacuum pump assembly, driven by a small, motorized operating vehicle. A suction hose runs from this unit into the pit, either through the squatting hole or a seat in the slab, or through a special opening directly into the pit. The excreta to be removed may be too solid for the pump to lift, so water may need to be added and the contents mixed to liquefy them first. Any stones, sticks, plastic bags and other solid items thrown into the pit will block the suction hose. Users need to be educated into what can and can’t be put into the pit, if this emptying option is to be used. Although the vehicle can access properties in densely-populated settlements, its small capacity and a speed limit of 4 km/hour makes for frequent trips and significant travel times to take excreta to a disposal site. Operators may resort to disposing the faecal sludge into a nearby watercourse or onto waste ground, if there is no provision for discharging into a sewer, or at a nearby treatment plant. Figure 6. UN-Habitat Vacutug However, the modified Vacutug (Mark II) subsequently developed operates with two units: a 1,900 litre main collection tank and a 200 litre unit. This ‘satellite’ unit can be pulled by a small tractor or pick-up, making access to densely- populated areas both easier and faster. In Dhaka, Bangladesh, demand for pit emptying services using the Vacutug Mark II has been steadily increasing in slums and squatter settlements, as well as for emptying septic tanks in middle- income areas. Finding suitable sites for sludge disposal remains an ongoing challenge (GHK, 2005). The Vacutug Mark II also has its limitations. The pit must be within 30m of the satellite unit for the suction pipe to reach into the pit, which can really only lift excreta from a maximum of 2m below ground.

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